Sweetening process



Patented Apr. 10, 1934 SWEETENING PROCESS Gentry Lloyd Rowsey, Big Spring, Tex.

No Drawing. Application March 13, 1930,

' Serial No. 435,656

4 Claims. (Cl. 19629) This is a continuation-in-part of my copendilragqapplication, Serial No. 183,624, filed April 13,

This invention relates to refining of hydrocarl bon oils; particularly to improvements in the refining of oils of the gasoline-kerosene type.

In refining gasolines and kerosenes, it has been common practice to agitate these oils with solutions containing litharge dissolved in an excess loof caustic soda. Such alkaline solutions of sodium plumbite form certain colored lead compounds which are oil-soluble but which are precipitated by the addition of free sulphur. To the extent to which the treated oils may contain elementary sulphur, such oil-soluble "lead compounds may be precipitated by this sulphur. In practically all cases, however, it is necessary after agitation with the alkaline sodium plumbite solution, to add free sulphur to break up these oil-soluble colored lead compounds and to efiect the removal of lead so combined as lead sulphide. This operation is commonly called sweetening.

There as several well recognized difiiculties incident to the method of sweetening just described. The cost of the reagents is frequently excessive; as much as a pound of litharge per barrel of gasoline or kerosene treated may be consumed in the operation. It is difiicult accurately to regulate the addition of free sulphur to the oil; usually a slight excess of free sulphur is left in the oil resulting in color instability and causing the oil to be corrosive with respect to metals such as copper; brass or bronze. The precipitate formed in the oil by the addition of sulphur, largely lead sulphide, is at first extremely fiocculent and voluminous and retains a considerable proportion of the oil. Much time is lost in effecting settling of these precipitates in order to permit a reasonably complete separation of the oil, and even under favorable conditions there is usually a substantial loss of the refined oil product in the precipitate. This precipitate is commonly discarded, although in some instances it is treated for the recovery of litharge or sodium plumbite to be used in subsequent operations. Other sweetening methods have been proposed; for example there have been proposals to effect the purpose of the sweetening operation by oxidation of the objectionable compounds, mainly sulphur derivatives, by various oxidizing agents and by absorption of such objectionable compounds on various absorbent materials such as silica gel, bauxite or absorbent 5 precipitates formed in the oil. In general, the

alkali plumbite method has been most generally used. My invention has, several important advantages over this common alkali plumbite sweetening operation.

According to my invention, the gasoline or 0- kerosene is treated with a solution of caustic alkali containing-suspended preformed lead" sulphide while subjected to the action of air brought into intimate contact with the oil and treating solution. The treatment may take place in'the presence of free sulphur, as in the method of treating with alkali plumbite described in the preceding paragraph. The alkaline solution may consist of caustic soda or a soda ash solution, although the caustic solution is ordinarily preferable. 'In carrying out my invention, it is advantageous to mix the oil and. treating solution together while blowing air therethrough under conditions such that the air is intimately distributed through the mixture in the .formof fine bubbles. It is also advantageous to employ a. treating solution containing suspended a dense pulverulent form of lead sulphide.

Lead sulphide precipitated in the usual sodium plumbite sweetening operation changes from the g0 bulky fiocculent form in which it is initally precipitated to a fine, dense powder-like material after standing for some time. This more dense material quickly settles out of oil with which it is agitated. I have found this relatively dense 5 pulverulent form of lead sulphide, formed when the precipitate in the ordinary sodium plumbite sweetening operation is permitted to stand, is a particularly advantageous form of lead sulphide for use in carrying out my present invention.

I have found that even extremely malodorous gasolines or kerosenes, containing for example suflicient sulphur containing impurities of the mercaptan type to have a very objectionable 5 odor and to cause large consumption of sodium plumbite in the ordinary sweetening operation, can be rendered entirely satisfactory as to odor and non-reactive to the sodium plumbite reagent in a very brief period of treatment by agitation with a suspension of lead sulphide in a caustic alkali solution in the presence of air introduced into and passed through the oil and treating solution in the form of fine bubbles. Subsequent to this treatment, the lead sulphide suspension is settled out of the oil. This settling is easily and quickly efiected if the form of lead sulphide described above is used. I

The alkaline suspension of lead sulphide separated from the oil after treatment can be used 119 replenish .the lead sulphide.

again for treatment of further quantities of the oil, and the activity of the lead sulphide apparently continues for an indefinite time. In the practice of my invention on an industrial scale, I have employed the same alkaline suspension of lead sulphide for periods of three or four weeks in the continuous treatment of successive quantities of raw gasoline without having to This is one of the important advantages of my invention; there is no large consumption of the active material, and this affords an important economy as compared to methods hitherto known, in which litharge is used for example.

I have found that intimate contacting of air with the lead sulphide suspension is essential, and that the effectiveness and rapidity of the treating operation is to a large extent promoted by promoting intimate contact between the mixture of oil and the treating solution and the air supplied to the operation.

I have also found that it is advantageous to found it advantageous to carry the operation out,

in the substantial absence of sodium plumbite to avoid any formation of such components.

The alkali in'the treating solution is consumed by the action of any dissolved hydrogen sulphide present in the oil subjected to treatment, and I have also found that the resulting alkali sulphides in the treating solution apparently retard the sweetening operation if present in sufiicient amount. Accordingly, I find it advantageous to give oils containing dissolved hydrogen sulphide a preliminary treatment with an alkaline solution,'for example with a solution containing the minimum proportion of caustic soda suflicient to remove such dissolved hydrogen sulphide.

As a specific example of the practice of my invention, I give below an operation carried out upon a very sour gasoline obtained from crude petroleum from the Panhandle field in Texas, commonly known as Panhandle crude: y

The gasolinetreated had a particularly high content of sulphur compounds of the mercaptan type, and when treated by the usual sodium plumbite method required about one pound of litharge and a correspondingly large proportion of sulphur per barrel (42 gallons). In a batch operation, in accordance with my invention, 1,000 barrels of this gasoline were treated with 100 barrels of a solution of caustic soda, about 15 B., containing about 1,500 pounds of previously prepared precipitated lead sulphide in suspension. This mixture was agitated by blowing air through it, and the air was introduced so as to form fine bubbles producing a froth which was carried up into and through the oil. After fifteen minutes agitation, the treating solution and suspended lead sulphide was allowed to settle out of the oil, and the oil separated'from the settled alkaline mixture. The separated oil was of entirely satisfactory odor and was non-reactive to sodium plumbite.

In the treatment of such gasolines in the man- ,ner just described, it is not unusual to find that there has also been a substantialimprovement in color, for example as much as one to two points on the Saybolt color scale.

' I have observed, in carrying out my invention. that the bubbles of air when in a sufiicien 1;. fine -close to the bottom of the cone. introduced the air in relatively small streams bestate of subdivision, become filmed over with I lead sulphide, the lead sulphide thus being carried up through the oil. And I find it advantageous in carrying out my invention to promote sub-division of the air introduced into the mixture of oil and treating solution. For this purpose, I have employed various forms of apparatus. For example, in the treatment of successive batches of oil, I have employed cone bottom agitators of conventional design'and have introduced the air in very fine streams or bubbles through a plurality of small orifices arranged I have also neath mechanical agitating devices such as a propeller or a propeller arranged to operate with in a sleeve. Theair may also be introduced by forcing it into the mixture of oil and treating solution through porous material, for example through a tube or plate of alundum or porous baked silica, forming very fine bubbles or a fine froth. In continuous operation, the oil and treating solution may be supplied to the lower end of a vertically arranged orifice mixer into the lower part of which the necessary air is also introduced.

I am not certain as to' the exact relationship of the effect of the air and the metallic sulphide in the alkaline solution in causing the sweetening action. The air and lead sulphide apparently react to a considerable extent, which may form alkaline thio-sulphate which then reacts with the sulphur compounds in the oil to assist in the sweetening action. Thus, the process may be applied in such manner that the suspension of lead sulphide in alkaline solution is blown with air, and the oilis then treated with the aerated suspension, whereby sweetening is effected. The suspension may be withdrawn and sepae rated from the oil, blown with air, and again applied to the oil-to efiect sweetening.

There also appears to be a direct oxidation of thesulphur compounds by the air when intimately admixed with .the oil being treated, the lead sulphide promoting the reaction. In any event, I ,do know that the action of the air on the lead sulphide suspended in the alkaline solution, or on.

' of gasolines and kerosenes in accordance with my invention does not usually involve any large reduction in sulphur content.

In commercial practice, I have found that, even in extreme cases, the use of inordinately large volumes of air is unnecessary. In many cases, for example, I have found the total volume of air required is not much more than about ten times the total volume of the oil treated, and frequently the proportion required is less than this. The proportion of air used, of course, is dependent upon the efliciency with which it is used, and

through one or more settling receptacles where the rate of flow is adjusted to promote separation of the oil from the treating solution. The facility with which the treating solution can be caused to separate from the oil in carrying out my invention makes it particularly valuable for continuous operation. Likewise, in continuous operation in accordance with my invention, the treated solution containing lead sulphide may be pumped directly from the bottom of the settling tanks back to the mixingapparatus. The treating solution, in such an operation, may be replaced from time to time, or a part of it may be continuously discharged and this part replaced by fresh treating solution.

In order to reduce any loss of gasoline or kerosene by evaporation, the air employed is advantageously recirculated, in whole or in part, until due to consumption of oxygen it becomes ineifective for the purposes of the treatment. Likewise, escaping air may be subjected to treatment for the recovery of any hydrocarbon vapors it may contain, for example by absorption treatment with active charcoal or with an absorbent oil, or by cooling and compression.

Although the lead sulphide may be used repeatedly, an indefinite number of times, its activity may be promoted by treatment, from time to time, with steam to remove any absorbed or entrained oils or oily impurities. Such treatment assists in making it possible to use a minimum of the lead sulphide or to reduce the time of treatment or to reduce the amount of air required.

Obviously many modifications and variations of the invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

I claim:

1. An improved method of sweetening gasolines and kerosenes which consists in intimately contacting a suspension of preformed lead sulphide in a caustic soda solution with air to activate it and under such conditions as to avoid the formationof substantial quantities of sodium plumbite, and then agitating the oil with the lead sulphide suspension so treated.

2. An improved method of sweetening gasolines and kerosenes which consists in intimately contacting a suspension of preformed lead sulphide in a soda ash solution with air to activate it and under such conditions as to avoid the formation of substantial quantities of sodium plumbite, and agitating the oil with the lead sulphide suspension so treated.

3. A continuous process of sweetening gasolines and kerosenes which consists in intimately contacting a suspension of preformed lead sulphide in a caustic soda solution with air to activate it and under such conditions as to avoid the formation of substantial quantities of sodium plumbite, agitating the oil with the lead sulphide suspension so treated, separating the lead sulphide suspension from the oil and again intimately contacting it with air to activate it and under such conditions as to avoid the formation of substantial quantities of sodium plumbite, and then agitating the lead sulphide suspension so treated with further oil.

4. An improved method of sweetening gasolines and kerosenes which consists in intimately contacting air and a suspension of preformed lead sulfide in an aqueous solution of a compound selected from the group comprising sodium hydroxide and sodium carbonate to activate it and under such conditions as to avoid the formation of substantial quantities of sodium plumbite, and then agitating the oil with the lead sulfide suspension so treated.

GENTRY LLOYD ROWSEY.

CERTIFICATE OF CORRECTION.

Patent No. 1,954, 103.

April it), 193 4,

GENTRY LLOYD ROW SEY.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 1, line 4, after "to" insert the; and line 55, after "general," insert however,;

page 3, line 105, after "oil" and before the comma insert to be sweetened; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 24th day of July, A. l). 1934,

Bryan M. Battey Acting Commissioner of Patents. 

